In devices such as keyboards, it is desirable that all or substantially all of the keys have the same spring rate, that is, that substantially all of the keys require the application of the same force to achieve a specified displacement of the keys. This uniformity of spring rate is comfortable for the key operator and tends to produce uniform print quality when the device is used for direct printing and to produce reliable data input when the device is used as a data entry terminal for a computer or the like. In addition to uniform spring rate, it is desirable that depression of the keys and their return to the normal position be achieved with a minimum of noise.
Generally, control of spring rate has heretofore been achieved by components that are attached between the key arms and the keyboard supporting structure. In U.S. Pat. No. 3,609,757, a retaining spring is used to regulate spring rate with compression of the spring returning the key arm to its normal position following depression. In U.S. Pat. No. 1,974,307, spring tension is utilized to achieve key spring rate control. The use of springs and other mechanical members to adjust spring rate and to achieve key return is not desirable because of the cost, noise and complexity of such arrangements. Although the unitary molded switching device described in U.S. Pat. No. 3,767,022, may obviate some switching-related noise problems, such devices still require independent means for returning the switch elements to their normal, or rest, position when the operator releases the depressed switching key.